Java G1 garbage collection in production

Question

Since Java 7 is going to use the new G1 garbage collection by default is Java going to be able to handle an order of magnitude larger heap without supposed \"devastating\" G

Answer 1

We are already using G1GC, from almost two years. Its doing great in our mission critical transaction processing system, and It proved to be a great support w.r.t high throughput, low pauses, concurrency and optimized heavy memory management.

We are using following JVM settings:

-server -Xms512m -Xmx3076m -XX:NewRatio=50 -XX:+HeapDumpOnOutOfMemoryError -XX:+UseG1GC -XX:+AggressiveOpts -XX:+UnlockExperimentalVMOptions -XX:MaxGCPauseMillis=400 -XX:GCPauseIntervalMillis=8000 -XX:+PrintGCTimeStamps -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCApplicationConcurrentTime

Updated

-d64 -server -Xss4m -Xms1024m -Xmx4096m -XX:NewRatio=50 -XX:+UseG1GC -XX:+UnlockExperimentalVMOptions -XX:+HeapDumpOnOutOfMemoryError -XX:-DisableExplicitGC -XX:+AggressiveOpts -Xnoclassgc -XX:+UseNUMA -XX:+UseFastAccessorMethods -XX:ReservedCodeCacheSize=48m -XX:+UseStringCache -XX:+UseStringDeduplication -XX:MaxGCPauseMillis=400 -XX:GCPauseIntervalMillis=8000

Answer 2

The G1 collector reduces the impact of full collections. If you have an application where you have already reduced the need for full collections, the Concurrent map Sweep collector is just as good and in my experience has shorter minor collection times.

Answer 3

I have recently migrated part of Twicsy to a new server with 128GB RAM and decided to use 1.7. I started off using all the same memory settings as I used with 1.6 (I have several instances running doing various things, anywhere from 500mb of heap up to 15GB, and now a new one with 40GB) and that did not work out well at all. 1.7 seems to use more heap than 1.6, and I experienced a lot of issues over the first few days. I luckily had plenty of RAM to work with and bumped up the RAM for most of my processes, but still was having some issues. My normal MO was to use a very small minimum heap size of 16m, even with a max heap of several gigabytes, then turn on incremental GC. This kept the pauses at a minimum. That doesn't work now though, and I had to increase the minimum size to about what I expected to use on average in the heap, and that has worked out very well. I still have incremental GC turned on, but I will be trying it without. No pauses whatsoever now, and things seem to be running very fast. So, I think the moral of the story is don't expect your memory settings to translate perfectly from 1.6 to 1.7.

Answer 4

I'm working with Java, for small and large Heap, and the question of the GC and Full GC appears every day, as the constraints may be more strict than others : in certain environment, 0.1 second of scavenger GC or Full GC, kill simply the fonctionnalité, and have fine grained configuration and capability is important (CMS, iCMS, others ... the target is here to have the best possible response time with the nearly real time treatment (here the real time treatment is often 25 ms ), so, basically, any improvements in GC ergonomy ans heuristique are welcome !

Answer 5

CMS can lead to slowly degraded performance even if you are running it without accumulating tenured objects. This is because of memory fragmentation which G1 supposedly avoids.

The myth about G1 available only with paid support is just that, a myth. Sun and now Oracle have clarified this on the JDK page.

Answer 6

I use G1GC on Java 8 and also with Groovy (also Java 8), and I am doing various kinds of workloads, and overally G1GC works like this:

• The memory usage is very low, e.g. 100MB instead of 500MB compared to default Java settings

• The response time is consistent and very low

• The performance between default settings and G1GC is 20% slowdown when using G1GC in worst case scenario (without tuning, single-threaded application). It's not much considering good response time and low memory usage.

• When running from Tomcat which is multi-threaded, the overall performance is 30% better and memory usage is much lower as well response times are much lower.

So in overall, when using really various workloads, G1GC is very good collector for Java 8 for multi-threaded applications, and even for single-threaded there are some benefits.